1. What must be your average speed in order to travel 230
km in 3.25 hours?

vav = Ds/Dt

distance = 230 km and time = 3.25 hours so average speed is
230/3.25, or 70.8 km/hr.(Table of contents)

3. If you are driving 110 km/hr along a straight road and
you look to the side for 2.0 sec, how far do you travel during this
period?

vav = Ds/Dt

The only tricky part of this problem is to remember to keep
your time units the same. Divide your speed in km/hr by 3.6 and you get
m/s.

110/3.6 = 30.555556 m/s

Now use 30.555556 as your velocity and 2.0 as your time and
solve for displacement. s = 61 m.(Table of contents)

5. You are driving home from school steadily at 65 mph
for 130 miles. It begins to rain and you slow to 55 mph. You arrive
home after driving 3 hours and 20 minutes. (a) How far is your hometown
from school? (b) What was your average speed?

(a) First, figure out how long it took to travel the
first 130 miles. v = s/t. v = 65 and s = 130. Solve for t
and you get that the first 130 miles took 2 hours. Since the whole trip
took 3 hours and 20 minutes, you know that 1 hour and 20 minutes was spent
driving in the rain at 55 mph. Since you know time (1.3333 hrs) and
speed (55 mph), you can figure out how much distance you covered in the second
part of the trip. v = s/t. v = 55 and t = 1.3. Solve for s
and you find that you drove 73.333 miles in the rain.

You can add these distances together to find out how far you
traveled altogether

73.333 + 130 = 203.333 miles = 203 miles

(b) Average speed is total distance/total time.
You just figured out the total distance (203.333 miles) and the total time was
given (3.3333 hours). Divide these two. Average speed = 60.999 mph
= 61 mph.(Table of contents)

7. A person jogs eight complete laps around a
quarter-mile track in a total time of 12.5 minutes. Calculate (a) the
average speed and (b) the average velocity.

The important thing to notice here is that average speed
means distance/time and average velocity means displacement/time.

(a) First we must figure out how much distance the
jogger covered. Eight times around .25 miles = 2 miles. The book
wants your answer in m/s so we must convert 2 miles to meters. 1 mile =
1.61 km, so 2 miles = 3.22 km. 3.22 km*1000 = 3220 m.

Now we need to know how much time it took. We need to
take the time they gave us (12.5 minutes) and convert it to
seconds.
12.5 * 60 = 750 sec.

(b) Now we have to consider the displacement, not the
distance. Remember that displacement means how far (and in what
direction) you are now from where you started. If someone jogs eight
complete laps, then they end up right where they first started. Since
displacement = 0, velocity = 0.(Table of contents)

9. Two locomotives approach each other on parallel
tracks. Each has a speed of 95 km/h with respect to the ground. If
they are initially 8.5 km apart, how long will it be before they reach each
other? (See Fig. 2-28)

<Fig 2-28>

Since their velocities are the same and they are headed
directly towards each other, we can logically assume that they will meet at a
point that is halfway between where they started. This point is 8.5/2 =
4.25 km away from each train. So all we really need to worry about is
how long it takes one train to travel 4.25 km.